1. Field of the Invention
This invention relates to a window unit having an improved frame sill which is mounted on the outside of an opening in a building wall.
2. Prior Art
Exterior window units have been widely used because they provide a high degree of thermal insulation, air-tightness, and sound insulation and yet they retain the pleasing appearance of window assemblies which are composed mainly of paper screen sashes and normally present in openings enclosed by building walls. The frame sills of the exterior window units have vertical mounting fins to be mated with and secured to exterior surfaces of the sills of the normally present window assemblies, the mounting fins having horizontal engaging flanges formed integrally therewith and projecting inwardly from fin top ends. The horizontal engaging flanges are secured to top surfaces of the sills of the pre-installed window assemblies. However, the integrally formed engaging flanges present difficulty since the exterior window units cannot be mounted snugly in position, especially where the side jambs of the pre-installed window assemblies are inclined relative to their vertical axis or otherwise deformed, as shown by the side jambs of FIG. 4 hereof.